Hardware/Battery Issue/Loss advanced question

My had brother hard a problem with his phone regarding his battery life. He claimed it drained too quick. So he bought a new phone.
After I had "accidendatlly" destroyed the eMMC of my nexus 4 (See this thread) he gave me the phone and told me if I could fix it that I can buy it for a sharp price form him.

I've replaced the battery with a newly bought one online and got the phone out of hibernation mode by connecting it with USB cable and doing the volume down + power button trick.

I've noticed some issues regarding the battery:
- The first time I rebooted it battery life went from 96% to 84%. This was when doing a factory reset (from the menu in android 4.2.2). This has occured once.

- Last night the phone was fully charged so I hooked it off the charger and turned it off. This morning I turn it on and I notice the battery is at 66%. Literally 1/3 of the battery life was lost when the phone was turned off.

Obviously, (I think) there's a loss inside the hardware of some kind. There's one piece of history attached to the phone.
My brother had it one month and dropped it on the floor and his screen was cracked. He then let the screen be replaced by a repair center. They did replace the screen and locked the screws from the battery with some kind of glue (i think) because it was very hard to loosen them.

My questions:
- What could have caused this? Can it be by something done by the repair shop (reversible?)
- In which part of the hardware is this (loss) most likely to occur? Or one can't know this?
- Would it be sensefull to disassemble the phone and replace the screen with the screen from my broken phone (the one with the broken eMMC chip), or is there 0% chance on success by doing this swap?
- Any suggetions on how to tackle this problem or is it just something I'll need to accept. (which is hard to accept, )

You should first try to charge it to 100%, then calibrate the battery (there's a little tool in the play store called BatteryCalibration). The percentage values are just approximate. Android knows the amount of mA the battery has when full and constantly checks the current as it drains to calculate the percentage left.
Calibrating the battery basically means deleting these statistic files to allow the system to start from scratch. You may need to do a few discharge/charge cycles until it is somewhat reliable.
If this doesn't help I assume the fault is hardware sided.

You should first try to charge it to 100%, then calibrate the battery (there's a little tool in the play store called BatteryCalibration). The percentage values are just approximate. Android knows the amount of mA the battery has when full and constantly checks the current as it drains to calculate the percentage left.
Calibrating the battery basically means deleting these statistic files to allow the system to start from scratch. You may need to do a few discharge/charge cycles until it is somewhat reliable.
If this doesn't help I assume the fault is hardware sided.

Sent from my Nexus 4 using xda app-developers app

Hi thanks for your Swift reply. ive checked the app out and i think it needs root. This phone hasnt been rooted yet so ill Get to it when i get home. Greetings.

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